A global 3-D chemistry-transport model STOCHEM has been employed to study trends in the mole fractions of methane,
carbon monoxide and ozone in baseline air masses entering Europe from the Atlantic Ocean over the period from 1990 to
2030. With a range of emission scenarios for man-made ozone precursor emission sources available, a wide range of model
trends were predicted for the period up to 2030. In the scenario based on current planned air pollution controls, IIASA CLE,
methane shows a strong upward trend, ozone shows a weaker upward trend, and carbon monoxide is approximately flat in
baseline air masses. In one of the more pessimistic IPCC SRES scenarios, A2, all three gases show future increases. However,
in the scenario based on maximum feasible emission reductions, IIASA MFR all three trace gases decline. By 2030, projected
climate change reduces the growth in CH4, but has insignificant effects on baseline CO and O3 in these simulations. Global or
hemispheric ozone precursor emissions and their controls exert a potentially large external influence on Europe’s air quality.
This influence is currently not taken into account in future European air quality policy formulation.